#include <boost/asio.hpp>
#include <iostream>

using asio::ip::udp;

class UdpServer {
public:
    UdpServer(asio::io_context& io_context, short port)
        : socket_(io_context, udp::endpoint(udp::v4(), port)) {
        do_receive();
    }

private:
    void do_receive() {
        socket_.async_receive_from(
            asio::buffer(data_, max_length), sender_endpoint_,
            [this](std::error_code ec, std::size_t bytes_recvd) {
                if (!ec && bytes_recvd > 0) {
                    do_send(bytes_recvd);
                } else {
                    do_receive();
                }
            });
    }

    void do_send(std::size_t length) {
        socket_.async_send_to(
            asio::buffer(data_, length), sender_endpoint_,
            [this](std::error_code /*ec*/, std::size_t /*bytes_sent*/) {
                do_receive();
            });
    }

    udp::socket socket_;
    udp::endpoint sender_endpoint_;
    enum { max_length = 1024 };
    char data_[max_length];
};

int main(int argc, char* argv[]) {
    try {
        if (argc != 2) {
            std::cerr << "Usage: udp_server <port>\n";
            return 1;
        }

        asio::io_context io_context;
        UdpServer server(io_context, std::atoi(argv[1]));
        io_context.run();
    } catch (std::exception& e) {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}
